The present technology relates to a memory device which is provided with a favorable storage element as a one-time programmable (OTP) element and to a reading method and a writing method with respect to such a memory device.
The OTP memory element is a non-volatile storage element which stores information even when a power source is turned off and various structures therefor such as fuse types and anti-fuse types have been proposed to date.
In a fuse type OTP element, for example, an information writing operation is performed by fusing a resistor by passing a large current with respect to a resistance element formed of polycrystal silicon or the like and changing a state between two electrodes from a short-circuited state to an open state.
On the other hand, in anti-fuse OTP elements, there are oxide film breakdown type elements which change a state between two electrodes from an open state to a short-circuited state by breaking down a dielectric body film by applying a dielectric breakdown voltage or more to a metal oxide semiconductor (MOS) type capacitor.
In addition, as anti-fuse OTP elements, there are elements which use the snap-back phenomenon of MOS transistors as illustrated in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-510203 described above. The snap-back phenomenon is a phenomenon where a strong pinch off force is forcibly generated and a large current flows between a source and a drain using a voltage which is lower than the breakdown voltage of a normal MOS transistor when a transistor is set to an on state by applying a predetermined voltage (a gate voltage) to a gate and then the gate voltage is lowered. In the OTP element of Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-510203, a PN junction is broken by a large current which flows during the snap-back phenomenon and there is a short circuit between the source and the drain as a result. That is, even in the OTP element, the information writing operation is performed by changing the state between the two electrodes from the open state to the short-circuited state.
Furthermore, an anti-fuse element which uses an MOS shape as in Japanese Unexamined Patent Application Publication No. 2012-174864 is also in the related art. Japanese Unexamined Patent Application Publication No. 2012-174864 discloses an OTP element in which a filament made of metal is formed between the drain and the source by applying a voltage of a threshold or more between a drain and a source of an MOS, generating heat using a large current which flows when a bond is broken, and melting a metal material close to a heating section.